<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<input id="one"> + <input id="two">
<span id="eq">=</span> <span id="v"></span>
<script>
    var oneInput = document.getElementById('one');
    var twoInput = document.getElementById('two');
    var eq = document.getElementById('eq');
    var v = document.getElementById('v');

    eq.onclick = function () {
        var one = oneInput.value
        var tow = twoInput.value
        v.innerText = (parseFloat(one) + parseFloat(tow))
    }
</script>
</body>
</html>